This invention relates generally to an electrical apparatus for automatically controlling peak demands and more particularly, it relates to an energy management system for limiting continuously the consumption of energy and leveling peak electrical demands in industrial plants, restaurants, and the like.
It is generally well known that central power stations or generation plants are opposed to peak load conditions caused by increased usage of power by its large number of customers since a greater amount of the installed capacity is required to accommodate the increased power demands occurring at that given time. In order to encourage its customers to limit or lower their power levels on demand, it has been generally noted that power stations apply a demand charge in addition to a regular schedule of rates for the energy utilized. In order to determine such demand charge, a maximum demand level meter is employed for indicating the maximum amount of energy consumption (highest average kilowatt demand) over any pre-determined interval, i.e., 15 or 30 minute time period. This is commonly referred to as "demand metering". Of course, this period of time varies depending upon the individual utility companies. The demand charge can sometimes add as much as 50 percent to the total cost of the electricity.
To maintain the electric charges at a reasonable level, it is necessary to keep the power demand level below a pre-determined maximum value. In many typical cases, a customer's power level can be separated into a base load and a controllable load. The base load is one which should not be dropped such as process loads in industrial plants. A controllable load is one that may be dropped for a momentary interval of time without any inconvenience, such as lighting, heating and cooling loads.
It would, therefore, be desirable to provide an energy management system for limiting continuously the consumption of energy and leveling of peak demands by disconnecting from a power source a plurality of individual equipment or controllable loads in a pre-selected pattern when the total load demand exceeds a pre-set limit. This system would permit selective limiting or disconnection from the power service on a non-priority basis of the various controllable loads. That is, no one individual equipment or controllable load in a restaurant would always be the first one to be dropped. Thus, new maximum demands are prevented from occurring thereby preventing a higher demand charge to effect dollar savings and maximum operating efficiency.
Further, it has been experienced that in typical commercial facilities utilized only during normal working hours in the day, the peak demands usually occur during the early morning hours when facilities are starting up. At other times during the day or in the night, the demand may not be as high. Thus, it would also be desirable to provide an energy management system with programmable means to enable a consumer to select the controllable loads and the periods of time in a day in which each of the controllable loads are connected to the power station. This would allow the consumer to maintain his permissible maximum demand to a lower value, thereby reducing further the utility charges and increasing the operational efficiency.